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Rock Wren Teetering on the Mainland?

Alarmist? Maybe, but we have long been concerned about the state of rock wren, and Megan Willans imparted some bad news in February 2013.

Megan checked out the intensively-trapped area in the Murchisons, and adult rock wren were seen where expected. However, Dan Palmer, Jo Hoare, Colin O’Donnell and Antje Leseberg monitored 21 nesting attempts in the Homer and Gertrude areas, and all failed. They confirmed stoat predation at at least 9 of the nests, and mouse predation at at least one. (And who knows what happened to unmonitored populations not benefiting from 1080 application in the mast event just gone?)

These results make it even more important that the translocation to Secretary Island in 2008-2010 funded by Fauna Recovery NZ will prove successful. Pleasingly, the 2013 survey on Secretary turned up no fewer than 62 unbanded birds. There were also at least three banded ones living on from the founder population established in 2008-2010. The survey also showed rock wren descending into lower-altitude areas of suitable habitat, indicating the island might have pretty decent ultimate carrying capacity. This is important because there are not really any other islands to try, unless we have another go on Anchor, or get radical and try an island with lowland habitat only, hoping that these subalpine specialists can niche-hop. Rock wren as surrogate for the extinct bush wren? That may well be getting ahead of ourselves, and I do have a little worry in the back of my mind about how few founder adults were found on Secretary. It should have been a bit higher, and it’s possible this might indicate the population oscillating, with some seasonal factor causing greater mortality than normal. Stoat numbers evidently continue at stubbornly high(ish) levels despite all the effort being put in to this big island. Time will tell.

So, yes, I think rock wren are hanging by a thread, and we hope the Secretary work is enough to avert disaster while other solutions are found.